The Internet Protocol (IP) multimedia subsystem (IMS), defined by the 3rd Generation Partnership Project (3GPP), is an architectural framework for implementing IP-based telephony and multimedia services. IMS defines a set of specifications that enables the convergence of voice, video, data and mobile technology over an all IP-based network infrastructure. In particular, IMS fills the gap between two of the most successful communication paradigms, cellular and Internet technology, by providing Internet services everywhere using cellular technology in a more efficient way. Session Initiation Protocol (SIP) is the main protocol for IMS. IMS aims to ensure that IMS applications work consistently across different network infrastructures.
Current IMS SIP call flow systems provide serial and lengthy steps to setup or tear down a SIP session between caller A and caller B. These IMS SIP sessions can originate from an IMS-capable device and terminate at another IMS-capable device, a public switched telephone network (PSTN) or a non-IMS wireless device. SIP setup and/or tear-down processes typically flow serially, with IMS network elements sending each other similar and redundant SIP message commands. These similar and redundant SIP message commands increase the number of SIP message steps to execute and, in turn, increase the time to setup and teardown a SIP session.